LOW TEMPERATURE CO-FIRED CERAMIC (LTCC) SYSTEM IN A PACKAGE (SiP) CONFIGURATIONS FOR MICROWAVE/MILLIMETER WAVE PACKAGING APPLICATIONS

ABSTRACT

Disclosed are methods and devices of microwave/millimeter wave package application.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. 119(e) to U.S.Provisional Application No. 61/590,253 filed Jan. 24, 2102 and U.S.Provisional Application No. 61/740,574 filed Dec. 21, 2012.

FIELD OF THE INVENTION

Disclosed are methods and devices of microwave/millimeter wave packageapplication.

BACKGROUND

Low Temperature Co-fired Ceramic (LTCC) technology is an electronicpackaging platform especially suitable for high frequency system levelpackaging applications. A typical LTCC circuit substrate is formed bylaminating multiple layers of ceramic tape under pressure and then firedat high temperatures in the range of 800 to 900 degrees C. On firing,LTCC forms a monolithic circuit containing electrical interconnectionsand provides for a highly reliable integrated circuit chip carrierplatform. Electrical interconnections on LTCC substrates are generallyformed by using thick film metallizations of gold, silver, or coppermetals. Being a ceramic material, LTCC is a high reliability system andalso has very good thermal properties in addition to extremely lowdielectric loss for electrical signals. LTCC has a coefficient ofthermal expansion (CTE) relatively close to that of semiconductormaterials used for fabricating chips thereby making high reliabilityflip chip attachment possible.

A transceiver is a system that combines the functions of a transmitterand receiver in the same circuit. A practical transceiver circuit isrealized with a set of Millimeter Wave Integrated Circuit (MMIC) chips,interconnect metallizations patterned according to strict geometricrequirements, passive components such as resistors, capacitors, andinductors, metal patterns forming antenna elements and arrays, andantenna networks. Each of these sub systems and components imposesomewhat conflicting performance requirements on package configurations.

State of the art transceiver packaging solutions use different materialswithin the same package due to differing requirements imposed by varioussubsystems. For example, reliable flip chip attachment require a ceramicsubstrate while good antenna performance required a low dielectricconstant and hence the use of organic laminates. The multi-materialpackaging approaches result in complex package configurations resultingin performance impairments and expensive solutions. Both higherperformance and lower cost can be realized if a single substratepackaging solution can be provided. The concepts described here offersuch high performance and lower cost package approaches.

SUMMARY

In a first embodiment, the invention is directed to an integratedcircuit package configuration including (a) an antenna system havingextending antenna elements; (b) a substrate having a first side, asecond side and network internal transmission lines continuous from thefirst side to the second side, wherein the antenna system is attached tothe first side and the second side defines at least one cavity; and (c)at least one monolithic microwave integrated circuit (MMIC) mounted inthe at least one cavity defined by the second side, wherein theextending antenna elements extend via the network of internaltransmission pathways of the substrate and contact the MMIC establishinga transceiver circuit.

In another embodiment, the invention is directed to a method forreceiving and transmitting a signal including (i) in an integratedcircuit package configuration receiving a first signal via the antennasystem; (ii) enabling power division and combination via the extendingantenna elements; (iii) providing phase shifting via the extendingantenna elements; and (iv) accepting a composite signal via steps (ii)and (iii) at the MMIC, wherein the first signal received is atmillimeter wave frequencies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view of a first embodiment of a package of the presentinvention attached to a mother board;

FIG. 1B is a plan view of the package of the first embodiment;

FIG. 2 illustrates the package substrate with flip chip attached MMIC;

FIG. 3 illustrates the package substrate with “double-cavity” and wirebond interconnect;

FIG. 4 illustrates the two-piece package substrate with an antennasubstrate and a chip substrate connected;

FIG. 5 is a plan view of a one-piece embodiment of the presentinvention;

FIG. 6 is a plan view the one-piece embodiment illustrating a steppedcavity and lid; and

FIG. 7 is a plan view of the one-piece embodiment illustrating wirebonding.

DETAILED DESCRIPTION

In a first embodiment, the invention described includes of twosubsystems—one chip carrier subsystem and another antennasubsystem—assembled together to form a single chip scale package. Thepackage configuration is suitable for microwave/millimeter wave systems(frequencies higher than 30 GHz). The package as described here forms afully integrated, self-contained transmitter/receiver (transceiver)system and antennas built on the same package. The following descriptionspecifically assumes Low Temperature Co-fired Ceramic (LTCC) as thedielectric material used for the package while any dielectric materialwith suitable electrical and mechanical properties (for example, LiquidCrystal Polymer (LCP) can be used in its place. General configurationsof proposed package structures are shown in figures below.

Referring to FIGS. 1A and 1B various aspects of a first embodiment ofthe invention are illustrated. In a first embodiment, the invention isdirected to an integrated circuit package configurations 10A 10Bincluding (a) an antenna system 12 having extending elements (notshown); (b) a substrate 14 having a first side 16, a second side 18 anda network of internal transmission lines 20 of via fill (metal) paste20A in the vertical direction and conductor pastes 20B in the horizontaldirection, continuous from the first side 16 to the second side 18,wherein the antenna system 12 is attached to the first side 16 and thesecond side 18 defines at least one cavity 22; and (c) at least onemonolithic microwave integrated circuit; “MMIC”, also referred to hereinas “chips” 24 mounted in the at least one cavity 22 defined by thesecond side 18, wherein the extending antenna elements extend via thenetwork of internal transmission lines 20 of the substrate 14 andcontact the MMIC 24 establishing a transceiver circuit.

The substrate 14 in the present embodiment is of LTCC but can be of anyother dielectric material with suitable dielectric and multilayerproperties such as Liquid Crystal Polymer (LCP). The cavity 22 depth canbe adjusted as necessary but needs to be at least 25% larger than theheight of the chips (including attachment structures) so that the MMIC24 can be completely situated within the cavity 22. The length and widthof the cavity 22 can be selected to accommodate all the MMIC 24 that areto be packaged to ensure easy access for the assembly equipment. Thebottom exterior surface 26 of the substrate 14 has the terminations 28required for necessary electrical, mechanical, and thermalinterconnections to external systems such as a general purpose PCB(printed circuit board) 1000. Without having to be limited theinterconnections to the external system are commonly ball grid array(BGA) balls mounted to the substrate to a printed circuit board.

Referring to FIG. 1A, electrical interconnections between the chips,between chips and BGA terminations, as well as between the chip and theantenna extending element subsystem are realized with controlledimpedance transmission lines 20 fabricated within the multilayer LTCCsubstrate 14. Internal transmission lines 20 are fabricated using thickfilm metal pastes either screen printed or patterned with laser ablationprocess on individual LTCC layers. Specially formulated via metal pastesare used for vertical interconnections between the conductors in eachlayer as customary in standard LTCC processing. Specially formulatedmeans that the thick film conductor pastes have specific amounts ofceramic, glass, metal, and organic components so that their electricalproperties are optimized for packaging applications. In addition suchpastes are formulated so that they have matching mechanical propertiesto that of the LTCC tape. Usage of multilayer LTCC substrate 14 alsoenables embedding passive components such as resistors and capacitorswithin the dielectric stack thereby significantly reducing the overallpackage size.

Referring to FIG. 1A, the interface between the antenna carriersubstrate portion 14A and the chip carrier substrate portion 14B can berealized by direct attach of the two substrates portions 14A, 14Bthrough solder or conductive epoxies or through controlled impedance BGAstructure. For this purpose ground-signal-ground pads for electricalinterconnection can be provided at specified locations predefined on thetwo LTCC substrates so that the two substrates portions 14A, 14B can bealigned together to form the overall package. In addition to theelectrical pads, additional mechanical and thermal management pads canbe used to enhance the mechanical strength (and to provide a highlythermally conductive path for heat dissipation) of the joint between thetwo substrates portions 14A, 14B so as to meet any required reliabilityperformance targets.

Chip Mounting and Interconnections

Referring to FIG. 2, the chip portion 14B of the package 100 isillustrated with MMIC 24 mounted on the second side (floor) 18 of thecavity 22. There are metal pads 30 (gold, silver, or copper) fabricatedby utilizing thin film or thick film deposition and patterning (such asvacuum deposition of thin film metals followed by photolithography andetching or screen printing of thick film metal pastes) techniques forchip attachment which can be either solder or conductive epoxy.

Referring to FIG. 3, in another aspect of this embodiment 10D, it isalso possible to attach the MMIC 24 in a “face up wire-bonded” 30Afashion. In this case there can be wire bond pads on cavity 22 floor 18.At millimeter wave frequencies it is critical to maintain the shortestpossible wire bond length along the signal path to reduce parasiticinductances which will severely restricts the performance of the chips.To alleviate this problem a “double cavity” approach as shown in FIG. 3can be used where the chips 24 are placed within a secondary cavity 22Afabricated within the first cavity 22 such that the wire bond pads 30Aon the chips 24 will be coplanar with the pads 30B on the floor of thefirst cavity 22. In the case of flip chip attached MMIC 24; it ispossible to use a suitable under fill material (not shown) to fill thespace between the bottom surface of the chips 24 and the cavity floor 18to ensure thermal expansion matching and hence higher reliability. Inaddition, the interior surfaces of the cavity 22 can be lined withsuitable microwave absorber materials to suppress unwanted cavityresonances.

Antenna Subsystem Description

All transceivers use some form of an antenna for transmitting and/orreceiving high frequency electrical signals. The invention describedhere uses a specific type of antenna structure called microstrip patchantenna which is formed by patterning metallization deposited or byprinting metallization on a suitable dielectric substrate. The nature ofmetallization, its geometry, the dielectric properties of the substratematerial etc. are some of the critical variable that determines theperformance of microstrip antennas. In general, the microstrip patchantennas used with the present invention can be a single patch elementof rectangular, circular, or any other geometrical shape, or a multitudeof such patch elements interconnected by suitably designed ‘network’forming an antenna array. Antenna elements are electrically connected tothe output section of such an array can be exclusively reserved fordifferent functions such as transmission or reception of signals. Incertain other applications the entire microstrip array can be used foreither transmission or reception at any given time. Electronic switchingcircuits can be added to the antenna system 12 to switch betweenfunctions when entire antenna is dedicated for one function at any giventime.

The antenna system 12 also enables power division/combination and phaseshifting functions which are essential for the operation of the antennaarray. Power divider circuit splits the output of the transmitter sothat a specified amount of power can be directed to each of the antenna“element”. The same circuit can be used in reverse for the receiver suchthat power received by each antenna element can be combined to form acomposite signal forming the input to receiver circuitry. Antenna arrayalso require a specified phase relationship between its individualelements. A phase shifter circuit can be used to realize this function.Both power divider/combiner and phase shifter circuits are generallyimplemented as interconnected discrete components such as resistors,capacitors, inductors, and integrated circuits.

Microstrip Antenna Design and Fabrication

Generally, microstrip antennas are fabricated by either patterningexisting metallization (subtractive process) or by depositingmetallization (additive process) on a high quality dielectric material.The dielectric material suitable for antenna implementations needs tohave the following characteristics; very low dielectric loss tangent(less than 0.005); relatively lower effective dielectric constant (lessthan 6); very tight dimensional control over substrate thickness +1-5%;and the ability to support antenna networks at millimeter wavefrequencies

Low Temperature Co-fired Ceramic dielectric technology provides anexcellent choice for antenna substrate since it meets all the criticalapplication. As discussed, this embodiment specifically describes anantenna subsystem fabricated on an LTCC multilayer substrate.

Antenna Patch Design and Realization

Any standard microstrip antenna design can be used in accordance withthe package configuration described herein. The metal patterns used forantenna elements can be realized by screen printing of thick film metalpastes on LTCC substrates with dielectric constant in the range of 4 to8 and loss tangent less than 0.004. In addition to screen printingeither vacuum deposited thin film or laser ablated metallizations can beused as well. Any typically used metallization choices from either thickfilm or thin film technologies including but not limited to gold,silver, and copper can be used for microstrip antennas. Also, eitherscreen printing, photolithography, laser ablation or a combination ofthese techniques can be used to realize the metal patterns. Radiatingpatch (in the case of single patch antenna) or elements (in the case ofan antenna array) can be located on either external surfaces of the LTCCslab forming the antenna substrate. In the embodiment 10E in FIG. 4, thecase in which the antenna system 12 is located on the external (top)surface of the substrate 14 is illustrated.

Antenna Substrate Choice

In the most general case any dielectric material suitable for highefficiency millimeter wave microstrip antennas can be used as thesubstrate. The substrate choice can include organic materials such asTeflon, Polyimide, and various epoxy resins or ceramic dielectricmaterials such as alumina, LTCC, aluminum nitride etc. LTCC as thesubstrate is preferred due to the following reasons: LTCC provides agood range of dielectric properties, dielectric constant in the range of4.5 to 8, very low loss tangent (less than 0.005), multilayer capabilityto simplify high density routing of interconnects, the ability to embedpassive components in the interior layers of the substrate so that theantenna can be integrated directly on the antenna substrate, and theability to fabricate integrated open and embedded cavities within thesubstrate enabling cavity-backed antenna structures. The presence ofsuch cavities—air pockets—under the antenna elements reduces theeffective dielectric constant of the substrate material. Hence,effective dielectric constant can get as low as 2.5 thereby increasingthe radiation efficiency of the antenna significantly.

In the invention disclosed herein the electronic components for thenetwork—both power combiner/divider and phase shifters—can either bediscrete devices attached to the external surfaces of the LTCCsubstrates or can be integrated as screen printed thick film basedcomponents on the internal layers of the LTCC substrate. The laterapproach significantly reduces the valuable surface area used by passivecomponents and results in significant reduction in the overall size ofthe package.

Network of Transmission Lines

As illustrated in FIGS. 1A-4, the network of internal transmission lines20 includes a group of controlled impedance electrical interconnectstransmitting electrical signals from the input/output terminals of thetransceiver circuit and antenna elements. In very simple antenna designsthe network can be a simple branch network of transmission interconnectswhich starts at the transceiver terminals as a single transmission lineand then divides in to multiple branches. The branching continues untilthe number of branched lines is equal to the number of antenna elementsand each branch line terminates at individual elements. In typicalimplementations of the antenna lines more functions are integratedbeyond typical signal interconnections. Power dividers and phaseshifters are electronic circuit comprised of components such asresistors, capacitors, inductors, and some in some cases integratedcircuits. In the presented embodiment such components can be eitherattached directly to the LTCC antenna substrate using solder orconductive epoxy; or can be integrated in to the internal layers of thesubstrate. In the latter case, resistive and capacitive thick film pastecompositions are used to screen print the required passive functionsduring the fabrication of the substrate.

The use of multilayer LTCC of the present embodiment 10A-10E variationsas illustrated in FIGS. 1A-4 as the antenna substrate makes it easier toroute the transmission lines forming the fee network since the internallayers of the substrate are available for such routing. In addition,mechanical punched or laser drilled via holes filled with suitable thickfilm conductive pastes are used for interconnecting various internalplanes of the LTCC along the vertical direction.

Referring to FIGS. 5, 6 and 7, n variations 110A, 1108, 110C of a secondembodiment, the LTCC substrate 114 is of one-piece design. FIG. 5describes the generic one-piece package configuration to enable therealization of specific functional requirements. All conceptconfigurations are built on multiple layers of LTCC substrate. Thespecific drawings are shown with 5 layers of 5 mil LTCC tape but theconfigurations are equally applicable to more complex circuits whichrequire may more layers—4 to 40 layers—and with 10 mil individual tapelayers. Referring to FIG. 5, a schematic diagram of the genericconfiguration is shown. The substrate 114 is built with five layers(marked “L”) of 5 mil 9K7 LTCC tape although other thicknesses, layercounts, and tape systems can be used. On the top surface a microstrippatch antenna array 112 with three elements are shown. For use with thepackage substrate 114 any planar antenna structure with a single elementor a large number of elements can be used. As in the previousembodiment, in addition to the rectangular shaped microstrip antennapatch (illustrated in FIG. 5) other shapes such as circular, triangle,or composite patches can be used as well. Individual antenna extendingelements (not shown) of the antenna system 112 are interconnectedthrough the network of internal transmission lines 120 by conductorpastes 120B with planar (horizontal) transmission lines as well asvertical interconnections via fill (metal) pastes 120A. The specificlocations, shapes, and other geometric details of metal patterns formingthis network can take many forms depending up the specific functionalityfor the circuit that is being packaged. As shown in FIG. 5, some of thevias are stacked on top of each other and some are used to connect metalpatterns on a single layer of LTCC dielectric. Similar to the previousembodiment, a rectangular cavity 122 is formed on the bottom of the LTCCsubstrate 114 and MMIC chips 124 are mounted using flip chip ball gridarray (BGA) 128 attachment on the floor of the cavity 122. The cavityshape can be generic such as circular or other odd shapes according todesign requirements. The cavity 122 is sealed with an optional lid 134for designs which require a sealed enclosure and/or hermetic sealing.The lid sealing can be realized with soldering or brazing the lid 134 toa metal frame (not shown) printed along the periphery of the cavity 122.As discussed, on the bottom 126 of the package 110 solder balls 128 areprovided to attach the package 110 to an organic printed circuit boardor another ceramic.

Referring to FIG. 6, another aspect of the variation of the secondembodiment 110 B describes a “stepped” cavity 122A. The addition of thestep on the cavity side wall provides a “ledge” or a “terrace” where thelid 134 can be attached. By this design total volume enclosed within thecavity 122A is significantly reduced there by decreasing chances ofdetrimental electromagnetic cavity resonances that can be excited in alarge size cavity 122 illustrated in FIG. 5. Presence of such cavityresonance can result in significant impairments to the electricalperformance of the package and their elimination is highly desired.

Referring to FIG. 7, a wire-bonded aspect 110C is illustrated in thestepped cavity 122A illustrated in FIG. 6. Presence of wire bonds 130can enhance the chances of excitation of high frequency cavityresonances and their elimination through the stepped cavity approach maybe necessary for achieving performance requirements.

As illustrated in FIGS. 5, 6 and 7, the package variations of the secondembodiment 110A, 110B, 110C depict a single piece, monolithic,multilayer ceramic packages which house an entire transceiver systemincluding integrated antennas. Such package design eliminates the needfor multiple materials to realize all the functions of a transceiver.FIGS. 5, 6 and 7 illustrate package concepts built from the same LTCCpanel since it is essentially a single piece LTCC part. This approachdoubles the throughput of the manufacturing line by design, leading tovery significant reduction in manufacturing cost and cycle time. Sincebuilt from a single piece of LTCC, there is no need to attach theantenna and chip carriers together with BGA (as discussed in the firstembodiment of the package 10A-10E) as it is a fully integratedstructure. The need for reflow process is completely avoided as well asthe complexity and cost associated with the assembly process. Noassembly is involved other than attaching the chip 124 and the lid 134.The aspects of this embodiment are packages with very high performance.Since the signals flow back and forth between chips 124 and antennas 112through fully shielded internal transmission lines 120 there is noadditional loss incurred due to BGA interface. Further, because thepackage of the present embodiment illustrated in FIGS. 5, 6 and 7 ismade of a single piece of ceramic materials, it results in an extremelyhigh reliability monolithic circuit. Even under harsh operatingenvironments and under heavy shock and vibration no performanceimpairment is expected; potentially due to being fully sealed hermeticpackages.

In another embodiment, the invention is directed to a method forreceiving and transmitting a signal including (i) in an integratedcircuit package configuration receiving a first signal via the antennasystem; (ii) enabling power division and combination via the extendingantenna elements; (iii) providing phase shifting via the extendingantenna elements; and (iv) accepting a composite signal via steps (ii)and (iii) at the MMIC, wherein the first signal received is atmillimeter wave frequencies. The substrate is a Low Temperature Co-firedceramic material.

To ensure quality and function of both the antenna and chip system, itis advantageous prior to step (i) to accessible components of theintegrated circuit package configuration. Specifically, in a multi-piecesubstrate, the ability to test the function of the package prior toconnecting the antenna and chip via the substrate is cost effective,results in higher end of the assembly line yield, and assures quality ofthe finished product.

As discussed in the previous embodiment, the ability to have a one-piecesubstrate allows, prior to step (i), configuring the extending antennaelements along the shortest distant between the MMIC and the antennasystem via the network of pathways of the substrate. Because anyadditional length of transmission line and package interfaces such asBGA transition will invariably result in more interconnects losses.Minimizing such losses is one of the primary objectives in any packagedesign.]

Additionally, as discussed in the previous embodiment and prior to step(i), formulating the electrical interconnections for use with thesubstrate will allow greater efficiency as the signal travels throughthe substrate of the finished product. Flow properties of the via fillpastes—especially the viscosity—needs to be carefully matched to thesintering properties of the LTCC tape during firing process to ensure agood contact formed by interdiffusion of materials components betweenthe tape and via fill paste. This is essential to achieve the requiredstrength for the tape-via interface. Similarly, sintering properties ofthe via fill paste and the conductor paste above and below the viamaking electric contacts need to be carefully matched so that highintegrity, void free electrical and mechanical contact is obtainedbetween these conductors. This is achieved through carefully engineeringthe material compositions of the said conductors and via fill pastematerials.

What is claimed is:
 1. An Intregrated circuit package configurationcomprising: (a) an antenna system having extending antenna elements; (b)a substrate having a first side, a second side and a network of internaltransmission lines continuos from the first side to the second side,wherein the antenna system is attached to the first side and the secondside defines at least one cavity; (c) at least one monolithic microwaveintegrated circuit (MMIC) mounted in the at least one cavity defined bythe second side, wherein the extending antenna elements extend via thenetwork of transmission lines of the substrate and contact the MMICestablishing a transceiver circuit.
 2. The package of claim 1, furthercomprising ball grid array (BGA) balls mounted to the substrate to aprinted circuit board.
 3. The package of claim 2, wherein the MMIC andthe antenna system are attached to the substrate using an attachmentmethod consisting of (i) solder attachment, (ii) conductive epoxyattachment, (iii) BGA attachment and (iv) wire bond attachment.
 4. Thepackage of claim 3, further comprising electrical interconnectionsspecifically formulated for use with the substrate.
 5. The package ofclaim 4, wherein the substrate is made of a dielectric materialconsisting of the group of a Low Temperature Co-fired Ceramic (LTCC) orLiquid Crystal Polymer (LCP)
 6. The package of claim 5, wherein the atleast one cavity has a depth of at least 25 percent greater than theheight of the MMIC.
 7. The package of claim 6, wherein the at least onecavity is a stepped form.
 8. The package of claim 7, wherein the atleast one cavity is sealed with a lid.
 9. The package of claim 8,wherein the seal is hermetic.
 10. The package of claim 9, wherein theMMIC has a frequency range of 10 to 120 GHz.
 11. The package of claim10, wherein the antenna system comprises a microstrip patch antenna. 12.The package of claim 11, wherein the substrate is one-piece.
 13. Thepackage of claim 11, wherein the substrate is multiple-piece layers. 14.A method for receiving and transmitting a signal comprising: (i) in aIntregrated circuit package configuration of claim 1, receiving a firstsignal via the antenna system; (ii) enabling power division andcombination via the extending antenna elements; (iii) providing phaseshifting via the extending antenna elements; and (iv) accepting acomposite signal via steps (ii) and (iii) at the MMIC, wherein the firstsignal received is at millimeter wave frequencies.
 15. The method ofclaim 14, wherein the substrate is a Low Temperature Co-fired ceramicmaterial.
 16. The method of claim 14, wherein prior to step (i) testingaccessible components of the integrated circuit package configuration.17. The method of claim 14, wherein prior to step (i) configuring theextending antenna elements along the shortest distant between the MMICand the antenna system via the network of pathways of the substrate. 18.The method of claim 15, wherein prior to step (i) formulating theconductor pastes as well as vertical interconnections via fill (metal)pastes for use with the substrate.